Automating Manufacturing Systems - Process Control and ...

plc basic functions - 15.2
Combinatorial Logic
- relay contacts and coils
Events
- timer instructions
- counter instructions
Data Handling
- moves
- mathematics
- conversions
Numerical Logic
- boolean operations
- comparisons
Lists
- shift registers/stacks
- sequencers
Program Control
- branching/looping
- immediate inputs/outputs
- fault/interrupt detection
Input and Output
- PID
- communications
- high speed counters
- ASCII string functions
Figure 15.1
Basic PLC Function Categories
Most of the functions will use PLC memory locations to get values, store values
and track function status. Most function will normally become active when the input is
true. But, some functions, such as TOF timers, can remain active when the input is off.
Other functions will only operate when the input goes from false to true, this is known as
positive edge triggered. Consider a counter that only counts when the input goes from
false to true, the length of time the input is true does not change the function behavior. A
negative edge triggered function would be triggered when the input goes from true to
false. Most functions are not edge triggered: unless stated assume functions are not edge
triggered.
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